Determining main carbonate mineralogy, and the primary components of the non carbonate fraction, at four depths in core GC12, collected from the Capricorn Channel.

A gravity core (GC12) was collected from a depth of 990.5 mbsl within the Capricorn Channel, southern Great Barrier Reef (GBR). Analysis of other parameters revealed the Last Glacial Maximum (LGM) sitting at a depth of ~175cm into the core. Four samples were collected for X-ray Diffraction (XRD) analysis; the top two, at the sediment surface (GC12-0) and at 30cm (GC12-30) represent interglacial sediment, while the lower two, at 210cm (GC12-210) and 330cm (GC12-330) represent glacial sediment. XRD analysis suggests that the majority of the carbonate is calcite during the interglacials, primarily from pelagic carbonate production. During the glacials and transitions more quartz, feldspar, aragonite and Mg calcite are present. This suggests that there is a changing dominance of pelagic, terrigenous and reef platform material within the core related to sea-level variations.

本次研究从大堡礁（Great Barrier Reef，GBR）南部摩羯水道内990.5米海平面以下（meters below sea level，mbsl）处采集了重力岩心GC12。通过对其他参数的分析可知，末次冰盛期（Last Glacial Maximum，LGM）位于该岩心约175厘米深度处。本次共采集4件样品用于X射线衍射（X-ray Diffraction，XRD）分析：其中表层沉积物样品GC12-0与30厘米深度样品GC12-30代表间冰期沉积，而210厘米深度样品GC12-210与330厘米深度样品GC12-330则代表冰期沉积。X射线衍射分析结果表明，间冰期沉积物中的碳酸盐以方解石为主，其主要来源于远洋碳酸盐沉积作用。在冰期及气候过渡阶段，沉积物中则赋存更多石英、长石、文石及镁方解石。上述结果表明，岩心中远洋物质、陆源物质与礁台物质的占比随海平面变化发生了动态更替。